In a field using an oxidatively polymerizable resin as a structural component, such as a printing ink and a coating material, a drier is added as a curing accelerator for drying the resin. As the drier used in the ink or the coating material, a metal salt of a heavy metal such as cobalt, manganese, lead, iron, or zinc and various carboxylic acids (hereinafter, may be abbreviated as “metal soap”) is generally used.
Particularly, a cobalt metal soap has excellent drying performance, however, in a case where a large amount thereof is used for obtaining higher drying performance, surface drying of an ink or a coating film may extremely rapidly proceed, and thus, the cobalt metal soap may be a reason of wrinkles or shrinkage. Therefore, as a method of obtaining high drying performance while preventing such wrinkles or shrinkage, a curing accelerator containing both of a cobalt metal soap and bipyridyl has been proposed (for example, see PTL 1). This curing accelerator prevented wrinkles or shrinkage and had high drying performance.
However, cobalt compounds are listed up in Group 2B of “possibly carcinogenic to humans” in the carcinogenicity risk list by the International Agency for Research on Cancer, and accordingly, carcinogenicity of the cobalt compounds is concerned. In addition, metal cobalt is a rare metal and supplying thereof is unstable, and accordingly, the price of the cobalt metal soap is high. Therefore, a curing accelerator having high drying performance in which no cobalt soap is used or a decreased amount of the cobalt metal soap is used is required.
As a method of preventing wrinkles or shrinkage without using the cobalt metal soap, a drying accelerator (curing accelerator) containing both of a manganese metal soap and bipyridyl is already proposed, before the curing accelerator is disclosed in PTL 1 (for example, see PTL 2). However, although the drying accelerator disclosed in PTL 2 is advantageous in that no cobalt metal soap is used, a drying time is increased in a case of being used as a curing accelerator of a printing ink or a coating material.
As a curing accelerator usable with a practical drying time, a use of both fatty acid manganese salt and specific amino alcohol has been proposed (for example, see PTLs 3 to 6), but curing properties comparable to those of the cobalt metal soap have not been obtained yet.
Meanwhile, as a curing catalyst of an oxidatively polymerizable compound including vegetable oil, a method of using a complex formed of a specific quadridentate ligand compound and metal has been proposed (for example, see PTL 7), and the vegetable oil is limited to a material containing 50% or more of phenol compounds such as anacardic acid, anagiganic acid, perranjic acid, ginkgotic acid, ginkgolinic acid, cardanol, cardol, methyl cardol, urushiol, thitsiol, renghol, and laccol, such as cashew nut shell liquid obtained from cashew trees. That is, a curing reaction using this complex occurs with a radical coupling reaction of a phenoxy radical generated due to dehydrogenation of a phenol compound, and accordingly, the complex cannot be used in a system including no phenol-based compounds. In addition, this complex has poor solubility in organic solvents, and thus, it is difficult to use the complex for compositions for general inks or coating materials. The complex is supposed to be formed in a system to cause a curing reaction, but it is necessary to use a material which is hard to handle outdoors, such as hydrogen peroxide water or ethylenediamine in the system, thereby causing poor versatility as well.